The Irish equine industry
Over many centuries, Ireland has become famous for its bloodstock. The country’s climate, soil and its peoples’ innate knowledge have given the Irish many advantages in the production of quality horses. These qualities continue to draw leading investors to our island, thus making the Irish bloodstock industry a major economic force.
The equine industry in Ireland is broken into two sectors: the thoroughbred bloodstock industry and the non-thoroughbred/sport horse industry. The thoroughbred industry is sub-divided into breeding and racing sectors with the former supplying the latter. These sectors of the industry are of vital economic importance to Ireland, as thoroughbred horses comprise the third largest export in the country. Contributions to the balance of trade through exports yielded £257.2 million from 1990- 1994 (Irish Horseracing Authority, 1999). This is due to the fact that 85% of all yearlings produced annually are exported (Weatherbys, 1999). The bloodstock industry has been experiencing a steady growth in the last two decades, producing employment directly and indirectly for 36,000-40,000 people and a disposable income of £70-£80 million (Central Statistics Office, 1999).
The non-thoroughbred/Irish sport horse sector is classified by the Central Statistics Office (1999) as ‘all non-thoroughbred horses and ponies kept or intended for farm work, for leisure or for sport’. Included are such breeds as the Irish Draught and Connemara. This sector is another large and economically important area. The industry had net exports of £4,776,890 in 1992 (Central Statistics Office, 1999), but it was observed that the official export figures were “seriously undervalued and a more realistic figure would probably be in the region of £16 million”. With a total of 8,971 persons employed directly and indirectly, and an average wage value of £19,762,081 per annum, this sector is also an important national revenue producer. While the thoroughbred and sport horse sectors (non-thoroughbred) are often regarded as two distinct industries, their paths, and inevitably, their fortunes, are closely linked.
Impact of moulds and mycotoxins on equine health
Moulds and their toxins are ubiquitous in nature, can cause potentially serious ill effects, and until recently have been generally ignored. Overlooking or disregarding fungal and mycotoxin causes, poor equine performance has usually been blamed solely on bacterial infections or injuries. How often have we heard a horse or horses described as ‘having the virus’? While these other conditions certainly exist, they are not always the sole reason for poor performance. Fungi and mycotoxins are capable of producing specific disease by themselves or in various combinations, but the end results are both serious and problematic. Identifying the sources of mould infections and their mycotoxins is now a prime function of our laboratory; and there is a growing realization that mycotoxins must be taken into consideration when tackling the problem of poor performance in the horse.
Respiratory problems are frequently either associated with, or exacerbated by, exposure to moulded feed. The horse is an incredible athlete but athletic performance can place extra demands on the respiratory system. A small amount of mucus in the airways can affect performance. The horse’s respiratory system is divided into upper and lower airways. The upper airways consist of the nasal passage, pharynx, larynx and the trachea and the lower consist of the lungs, bronchi, alveoli and capillaries. A common condition in horses is Chronic Obstructive Pulmonary Disease (COPD) also known as ‘Heaves’, which is an allergic disease similar to asthma in humans. Fungal spores, originating from dust, hay, bedding and feed, are the most common cause of COPD. When inhaled or ingested in sufficient quantity, these spores can cause inflammation and irritation of the small airways, thus leading to poor performance. Fungal contaminated feeds, forage and bedding can cause primary allergic and inflammatory disease and can also result in bleeding, often referred to as ‘bursting’.
Fungal contaminated feeds and forage can contribute to a range of other disorders in the horse. In addition to contributing to COPD and Exercise Induced Pulmonary Haemorrhage (EIPH), exposure to mould influences the incidence, severity and duration of episodes of infectious respiratory disease (Clarke, 1993). Inhaled respiratory particles have been shown to compromise the respiratory system’s ability to clear inhaled contaminants, including bacteria, from the lung (Ehrlich, 1980). Likewise, infectious respiratory disease can lower the lung’s tolerance to inhaled contaminants (Willoughby et al., 1991).
Mycotoxins can cause reproductive, respiratory, gastrointestinal and other disorders in livestock including the horse. Immunosuppressant effects of ingested fungal mycotoxins can also induce secondary mycotoxic diseases. It has been shown that impairment of immunity against bacterial and parasitic infections increased after consumption of mycotoxins as well as susceptibility to disease. Toxins produced by fungi such as Aspergillus spp., Fusarium, Penicillium and others are well recognised and identified in compounded feeds and feed ingredients fed in the poultry or pig industries. However, their importance and relevance in the equine sector has only recently been recognised, and names like aflatoxin, ochratoxin, vomitoxin (DON) citrinin, zearalenone, T2-toxin and others are becoming increasingly familiar as complications and compromised health or performance are being attributed to mould and mycotoxin problems.
Aspergillus and Fusarium toxins
The three most important toxigenic fungi are species of the Aspergillus, Fusarium and Penicillium genera. Aspergillus spp. are primarily thought of as spoilage organisms of stored cereals (Christensen, 1987), but may infect and produce aflatoxins in cereals in the field (Griffin et al., 2001). Barney et al. (1995) reported that 2.9% of field collected grains contained A. flavus and 2.1% contained A. fumigatus.
Aflatoxins, produced by certain Aspergillus spp. are potent liver toxins, and are known to be carcinogenic. Storage conditions can affect concentrations of aflatoxins in stored grain (Hell et al., 2000). This species may be very problematic, causing spoilage and disease in a number of ways. Control of growth and toxin production may be the best way to combat this problem, therefore an understanding of the conditions under which these occur is essential to effective prevention.
Aspergillus fumigatus is important in equine health due to its association with COPD. In horses COPD is thought to be a delayed hypersensitivity reaction to inhaled antigens, in particular to thermophilic moulds and actinomycetes that grow on damp hay. This disease is provoked by stable dust inhalation, particularly of fungal spores like those produced by A. fumigatus (Webster et al., 1987). Respirable particles are those particles below 5-10 μm in size (Dunlea and Dodd, 1995). Spores of A. fumigatus have an equivalent aerodynamic diameter of 3.11 μm (Clarke and Madelin, 1987) and are highly antigenic (Webster et al., 1987). A. fumigatus has also been found in hay, shavings and straw collected from stables by Clarke and Madelin (1987).
Fusarium toxins are produced by a large number of species, many of which produce more than one toxin. As well as producing mycotoxins, some Fusarium species are pathogens of plants, including those that produce our cereal grains. If conditions are favourable, and they very often are quite favourable, Fusarium may also act as a spoilage organism. It also occurs in soil and has been isolated from humans and animals with various health problems.
The fusariotoxins considered most important in animal health are fumonisins, fusaric acid, zearalenone and its derivatives, and the trichothecenes. A common feature of many Fusarium species is their ability to synthesise zearalenone, and its co-occurrence with certain trichothecenes raises important issues regarding synergism in the aetiology of mycotoxicosis in animals (Placinta et al., 1999).
Sources of moulds and fungal toxins
Certain fungi are present in the field before harvest and can proliferate if moisture content remains high due to inadequate processing and storage conditions. Mould, and subsequent mycotoxin contamination of a forage or feed, can increase in extreme environmental conditions such as drought or rain, followed by cold weather, or from mechanical damage to the forage or feed. Climatic conditions such as those in Ireland, damp and mild, can make it difficult to properly cure hay in the field.
The primary sources of mould infection are the feed and the bedding with which horses come into intimate contact, particularly hay and straw. Water supplies do not generally play an important function as a vehicle for these microorganisms, but the water offered to horses may become contaminated, thereby acting as a secondary source of infection – just like the atmosphere, various surfaces, feeding equipment and feed storage areas. Augers or corners in such feeding equipment as bins and hoppers, are thus a potent reservoir of contamination.
The relationship between amounts of mould growth and toxin production is complex. Massive mould growth may not necessarily result in high mycotoxin production, and seemingly minor concentrations of mould organisms can result in a toxic response. In addition, toxins have synergistic effects. For example, citrinin, which alone causes little overall damage in animals, in combination with other toxins in equally small amounts can produce severely detrimental results. It is also important to note that mycotoxin compounds are extremely stable to feed processing and so remain even when the producing organism is dead.
It is important to consider the conditions under which growth of these fungi occurs and those under which they produce the mycotoxins of interest. This is in order to ascertain suitable storage conditions for feeds and forages (Barney et al., 1995). The main factors which influence fungal growth and toxin production include:
• Moisture content / water activity
• Competition or interaction between fungi and other microorganisms
Of these factors, it is feed and bedding moisture content that is most often problematic. It is well recognised that feed moisture content significantly above 11%, which can ‘normally’ occur in most feeding systems and regimes, can lead to an explosion of mould growth and mycotoxin production. It can therefore be readily appreciated that anything that increases moisture level of rations or feed ingredients can represent a serious threat to equine health, vaccine responses or antibiotic therapy results. Cereals, especially maize imported from the US, can have water added to bring it up to 15% moisture. Feeding practices also have a big impact on moisture content. On many farms the feed, by the time it finally gets to the animal, can contain more than 20% moisture. The regular practice of soaking some feeds overnight to get horses to eat better has many pitfalls.
Irish Equine Centre mould and mycotoxin survey
During the past few years, the Irish Equine Centre has investigated a large number of premises that proved to have animals with fungal/mycotoxin infections. The affected animals all presented with similar symptoms, the most notable being poor performance or lack of performance, fatigue, continually high total bilirubin, low globulin values, gut-related problems, anaemia in some instances, and elevated muscle enzymes. On examination of these animals, there was no evidence of viral, bacterial or parasitic infection. The next step was to carry out a complete investigation of the premises concerned from an environmental point of view. Each of the premises had a full investigation, which included: (a) environment, (b) food, (c) bedding, and (d) animals.
The environmental samples taken included wall surfaces, air samples from inside the stable or in the case of American-style barns, from passages. Swabs were taken from around the feed and drink pots. The feed shed was also swabbed and the air sampled.
The samples of feed and bedding from the various premises were collected and analysed for the presence of fungi and mycotoxins in the laboratory using the ELISA method (Veratox® supplied by Neogen Corporation, US). Blood samples and bronchoalveolar lavages were taken by a veterinarian, and subsequently analysed for the presence of fungi and mycotoxins using the ELISA technique.
The Veratox mycotoxin kits are used for the quantitative analysis of mycotoxins in such commodities as mixed feeds, bedding, bloods and bronchoalveolar lavages. The test is a direct ELISA in a microwell format that allows the user to obtain exact concentrations in parts per billion (ppb). Free mycotoxin in the sample and controls is allowed to compete with enzyme-labelled conjugate for the antibody binding sites. The test is read using a microwell reader to yield optical densities. The optical densities of the controls form the standard curve, and the sample optical densities are plotted against the curve to calculate the exact concentration of mycotoxin.
Samples of food included hay and compound feed on arrival and on mixing and storing. Samples of bedding were taken in all cases. The animals were blood sampled for the detection of Aspergillus antigens in serum. Samples were cultured for bacteria and fungi. In all cases, the most commonly isolated microorganism was Aspergillus (Tables 1 and 2). On examination of the blood samples, antigens to Aspergillus were detected in approximately 60% of cases.
The study of fungi and mycotoxins is now an important part of our normal routine for the investigation of poor performance. A full service in this area is now offered to a range of clients in Ireland and Britain.
Although the pathogenicity of certain fungi has been recognised since the first half of the nineteenth century, laboratory expertise in the handling of clinical specimens and in the subsequent isolation and identification of the causative agents of fungal disease has been developed only in comparatively recent years. It is recognised now that the mycoses, diseases of fungal origin, are more common thanbefore; and their incidence has increased through the widespread use of antibacterial agents and immunosuppressive drugs. It is incumbent on microbiologists, therefore, to become more knowledgeable about the pathogenic fungi and their identifying characteristics.
Table 1. Results of sampling survey of five farm environments: positive or negative for presence of Aspergillus.
Table 2. Results of sampling survey of animals on five farms.
Barney, R.J., B.D. Price, J.D. Sedlacek and M. Siddiqui. 1995. Fungal species composition and abundance on stored corn as influenced by several management practices and maize weevil (Coleoptera:Currulionidae). Crop Production 14(2):159-164.
Christensen, C.M. 1987. Field and storage fungi. In: Food and Beverage Mycology (L.R. Beuchat, ed). 2nd edition New York, Workingham Van Nostrand Reinhold, pp. 211-231.
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Hell, K., K.F. Cardwell, M. Setamou and H.M. Poeling. 2000. Influence of storage practices on aflatoxin contamination in maize in four agroecological zones of Benin, West Africa. J. Stored Prod. Res. 36(4):365-382.
Placinta, C.M., J.P.F. D’Mello and A.M.C. MacDonald. 1999. A review of worldwide contamination of cereal grains and animal feed with Fusarium mycotoxins. Anim. Feed Sci. and Tech. 78(1-2):21-37.
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Webster, A.J.F., A.F. Clarke, T.M. Madelin and C.M. Wathes. 1987. Air hygiene in stables 1: Effects of stable design, ventilation and management on the concentration of Respirable dust. Equine Vet. J. 19(5):448-453.
Willoughby, R.A., G.L. Ecker, S.L. McKee and L.J. Riddols. 1991. Use of scintigraphy for the determination of mucociliary clearance rates in normal, sedated, diseased and exercised horses. Can. J. Vet. Res. 55: 315-320.
Author: THOMAS C. BUCKLEY
Irish Equine Centre, Co. Kildare, Ireland